The present invention relates to data transmission systems for transmitting data from a transmitter to a receiver over a communication link and, more specifically, to such systems for transmitting serially arranged binary information in message frame groups.
Many industrial control systems require the cooperative control of a plurality of related functions. These functions may be located proximate to one another, or, as is more common, remotely located from one another. In many cases, the overall control is achieved by means of a plurality of control units each of which is connected to a data unit. These data units may have, for example, buffer, translation, and isolation circuits, and/or storage registers, which are adapted to store digital data or digital data which is representative of analog data. It is generally desirable to update the various data units so that the entire control system operates in response to the latest available data. To accomplish this, it is necessary to provide a data transmission system between corresponding data units.
It is an overall requirement of any data transmission system for transmitting data from a first data unit to a second data unit, that the second data unit be undated in an efficient and reliable manner. To this end, a data transmission system must be able to address the first data unit; form the addressed data into a transmission format; include data identifying and verifying information; verify the transmission format at the second data unit; and address and update the corresponding data storing locations of the second data unit.
Data transmission systems meeting these requirements generally include a transmitter connected by a communication link to a receiver. The transmitter is adapted to cyclically address a first data unit and form the data addressed into message groups which also include message identity information, error and validity information, and data address information. The receiver is adapted to recognize each message, evaluate the validity of the message, and address the data to a second data unit in response to the reception of a valid message.
The present invention provides an improved transmission system which meets the above requirements and is adapted to reliably and efficiently transmit data between data units.